1. Field of the Invention
The invention relates to an apparatus of monitoring particles generated in fabrication of a semiconductor device, through the use of a laser beam, and a method of doing the same. More particularly, the invention relates to such an apparatus which is capable of monitoring particles at real-time by utilizing a scattered laser beam, and a method of doing the same.
2. Description of the Related Art
While a semiconductor device is being fabricated, there are generated particles such as dusts in a fabrication room. If such particles are adhered to a semiconductor device, performances of the semiconductor device would be much deteriorated. Hence, various apparatuses for monitoring particles have been developed in order to know the reason why such particles are generated in a fabrication room or the mechanism of generating such particles, or control an apparatus for fabricating a semiconductor device, to depress generation of such particles.
Examples of a particle monitoring system are described in Journal of Vacuum Science and Technology, Vol. B9, 1991, pp. 3487–3492, and Journal of Vacuum Science and Technology, Vol. A14, 1996, pp. 649–654, both written by Gary S. Selwyn.
The above-mentioned particle monitoring system is illustrated in FIG. 1.
As illustrated in FIG. 1, the particle monitoring system is comprised of a reaction chamber 15 formed with an beam-introduction window 16 and a detection window 17, a laser beam source 11, an oscillation mirror 13 reflecting a laser beam radiated from the laser beam source 11 into the reaction chamber 15, a photodetector 12 detecting a laser beam scattered by particles 19 existing in the reaction chamber 15, and a beam damper 18 absorbing a laser beam radiated from the laser beam source 11 and not scattered by the particles 19.
The particle monitoring system operates as follows.
A laser beam radiated from the laser beam source 11 is reflected at the oscillation mirror 13, and directed into the reaction chamber 15 through the introduction window 16. When the laser beam collides with the particles 19, the laser beam is scattered. The scattered laser beam is detected by the photodetector 12 such as a charge coupled device (CCD) camera through the detection window 17.
The detected scattered laser beam is recorded as a dynamic image indicative of the time at which the laser beam was scattered, and how an intensity of the scattered laser beam varied. Thus, it is possible to know how the particles 19 have been generated.
Apart from the above-mentioned particle monitoring system, an apparatus and/or method of monitoring particles generated in a room in which a semiconductor device is to be fabricated are suggested in Japanese Unexamined Patent Publications Nos. 4-54440, 5-273110, 6-82358, 9-243549, and 7-55692.
Japanese Unexamined Patent Publication No. 4-54440 has suggested an apparatus for monitoring particles, in which two laser beams are scanned by means of a rotary mirror. The laser beams having been scattered by particles are detected by a photodetector, and presence or absence of particles and speed of particles are measured based on the detection.
Japanese Unexamined Patent Publication No. 5-273110 has suggested an apparatus for measuring a diameter of a particle sufficient small relative to a wavelength of a laser beam. In the apparatus, a maximum scattering intensity is measured based on scattering intensity of each of pixels, using image data of scattered laser beams. Then, a diameter of a particle is calculated, based on the fact that an integration scattering intensity is in proportion to both the maximum scattering intensity and sixth power of a diameter of a particle.
Japanese Unexamined Patent Publication No. 6-82358 has suggested an apparatus for monitoring particles. In the apparatus, red, green and blue laser beams are radiated to particles. A size of a particle can be calculated based on how the laser beams are scattered in dependence on a wavelength of the laser beams and a size of a particle. Observing a color of the scattered laser beam through a monitor television, a size of a particle is measured.
Japanese Unexamined Patent Publication No. 9-243549 has suggested a method of monitoring particles. Laser beams are scanned to particles, and then, the laser beams having been scattered by particles are detected. In accordance with the method, data about three-dimensional distribution of particles can be obtained by means of a plurality of laser beam sources and a plurality of photodetectors for detecting scattered laser beams.
Japanese Unexamined Patent Publication No. 7-55692 has suggested an apparatus for monitoring particles, including a first vacuum chamber formed around a second vacuum chamber in which a semiconductor device is fabricated. The first vacuum chamber is in fluid communication with the second chamber, and is formed with a first window through which a laser beam is introduced thereinto and a second window through which a scattered laser beam leaves the first vacuum chamber.
In order to effectively control behavior of particles generated in a room in which a semiconductor device is fabricated, it is necessary to know data about a size and the number of particles in a real-time.
However, the above-mentioned particle monitoring system is accompanied with a problem that since particles are monitored through dynamic images of the detected, scattered laser beam, if images of particle are quite complex in the dynamic images, it would be quite difficult to obtain data about a size and the number of particles in a real-time.
Though the apparatus suggested in Japanese Unexamined Patent Publication No. 4-54440 can detect presence or absence of particles and a speed of particles, the apparatus cannot detect a size of individual particles which is a key for realizing the reason why particles are generated.
In the apparatus suggested in Japanese Unexamined Patent Publication No. 5-273110, it is necessary to calculate a sixth power root of the maximum scattering intensity in order to calculate a size of a particle, based on the measured maximum scattering intensity.
In the apparatus suggested in Japanese Unexamined Patent Publication No. 6-82358, data about a size of a particle is obtained in accordance with a color displayed in a monitor television. Accordingly, if obtained images of particles are complicated, it would be quite difficult to accurately grasp a size of a particle. In addition, a complicated device would be necessary for analyzing a color, and hence, it would take much time to analyze a color, resulting in that it would be impossible to have data about particles in a real-time.
The method suggested in Japanese Unexamined Patent Publication No. 9-243549 is accompanied with a problem that an apparatus used in the method cannot avoid to be large in a size, because the apparatus has to include a plurality of laser beam sources and a plurality of photodetectors.
The apparatus suggested in Japanese Unexamined Patent Publication No. 7-55692 is accompanied with a problem that the first vacuum chamber has to be additionally formed apart from the second vacuum chamber in which a semiconductor device is fabricated.